Flat panel displays as they appear in the marketplace today are generally all constructed on glass substrates. Liquid crystal displays (LCDs) that hold the greatest market share are fabricated using two glass substrates with liquid crystalline material sandwiched in between. In recent years there has been considerable interest in fabricating LCDs as well as other technologies on substrates that are flexible such as plastic or even drapable such as fabric. Such substrates are not so easily broken, are lighter in weight, and can be flexed, bent or made conformable to specific shapes and hold potential for lower cost roll-to-roll or sheet-to-sheet manufacturing.
In most of the LCD examples above, the bulk of the drive and control electronic circuitry is on a printed circuit board (PCB) that is typically separate from the glass display cell but mechanically attached via a bezel and some type of flexible cable, conductive elastomer, or metal pins to make electrical connections. Interconnects between the drive electronics and the display cell are one of the most labor intensive, intricate, fragile and problematic components of a flat panel display and its manufacturing. Some reduction in the number of interconnects is made with chip on glass type construction where the drive chips, for example, may be physically attached to the glass substrates.
More recently, efforts to construct displays on flexible substrates such as plastic have made the interconnect issue more problematic than ever in that interconnects must also be flexible if the same construction designs are employed that were used on glass displays. This has prompted other types of interconnect and display cell designs.
Contact strips on the flexible display have been disclosed as an interconnect means. U.S. Pat. No. 5,751,257 discloses a two-substrate flexible cell design for a shelf tag with a contact strip connected to the display electrodes. External electronic drive electronics are connected to the display through the contact strip. In a similar fashion, a contact strip is used in U.S. Pat. No. 4,948,232 to connect a large format two-substrate flexible display to an external drive apparatus. U.S. Pat. No. 4,896,946 discloses a two-substrate flexible display connected to a circuit board via a conductive adhesive contact strip.
U.S. Pat. No. 6,864,435 discloses a display design for a flexible smart card where conductors on the back surface of the display substrate are connected to integrated driver and other circuits as well as the column electrodes on the top side of the substrate using holes filled with a conductive material. The holes are laser drilled through the substrate to the electrodes and conductive material on the back of the substrate. The electrodes on the back side of the substrate can be patterned before or after the holes are made and used to make connections to the smart card contact pins. Drive circuits are deposited on the top side of the flexible substrate through a fluidic self-assembly process or other processes as may be used for organic light emitting diodes (“OLEDs”) or polymer light emitting diodes (“PLEDs”) or certain types of liquid crystal displays utilizing two substrates. In the case of the liquid crystal displays, row electrodes are on a separate cover substrate and are connected to the row drivers through conventional techniques for forming interconnects between the cover and bottom substrate.
Published patent application, U.S. Patent Application Publication No. 2003/0202136, discloses a cholesteric liquid crystal display fabricated on a single flexible substrate; however, the substrate is transparent. Since the display is viewed through the transparent substrate, the conducting elements of the display are applied to the back side of the transparent substrate. A support is located at the back of the display and makes electrical contacts so that the display is addressable from the front.
In this invention disclosed is a means of interconnecting to a single substrate; but, the substrate is the circuit board itself, containing drive and control electronics. In this case the substrate does not have to be transparent. The display elements are coated, printed or laminated on the circuit board substrate with the display electrodes connected to conductive pads on the substrate that are electrically connected to circuitry on the back of the circuit board.